The present invention relates to a backpack to be carried by a human and more particularly relates to a backpack frame for carrying relatively large loads while providing good stability and allowing substantial freedom of movement for the wearer.
Campers, alpinists, military personnel, and the like have long used backpacks to physically transport large loads over long distances and/or rough terrains. Typical of such backpacks are those which include a pack frame for suspending the load on the back of the wearer. Conventional pack frames employ shoulder straps to hold the backpack up in position on the back of the wearer. Such straps, however, also introduce a forward tension which counteracts the overturning moment of the pack and keeps the pack from toppling over backward. This continuous tension from the shoulder straps interferes with blood circulation under the straps, and results in a sustained tension in the shoulder and chest muscles. Accordingly, if only the shoulders and the upper back are used in carrying large loads, the discomfort to a wearer caused by shoulder straps of conventional packs can become excessive.
To alleviate this problem, many modern pack frames now include an elongated, board-like member which along with additional structure, straps, and/or padding distribute a part of the vertical component of the load to a belt-like structure worn about the hips of the wearer. This distribution of load appreciably decreases the shoulder tension and produces a lower resultant coupling to the body of the wearer thereby improving the wearer's dynamic stability and ability to maintain balance under rough conditions.
However, known means used in backpacks for distributing the load between the shoulders and hips have tended to interfere with the wearer's inherent counter-rotative body motions and have had an adverse effect on the wearer's ability to maintain balance while walking under pack, especially on terrain with a changing contour. This interference with normal body motions can also produce cyclic impulsive loading at the shoulder strap and hip contact points which, in turn, may lead to muscle soreness, cramps or chafing and even bruises under severe circumstances.